1. Field of the Invention
This invention relates generally to power supplies and more particularly to circuits for controlling the output of power supplies within previously defined voltage and current limits so as to prevent damage to both the source of power being supplied and the devices to which the power is supplied.
2. Description of the Prior Art
Foldback circuits for use with current limited or voltage limited power supplies are known in the prior art and typically employ conventional operational amplifiers, integrated circuits, and the like to achieve a foldback of operating current to within one-third to two-thirds of the normal full operating load current of the power supply. This foldback condition in the prior art is typically achieved using a nearly linear analog scheme to achieve a foldback of current during an apparent short fault in the output of the supply. One problem of this analog type of scheme is that the holding of this nominal current level can maintain current conditions which might harm circuitry powered by the power supply. The nominal level of current achieved during foldback condition typically varies significantly and is not predictable thereby further resulting in potential damage to the output electronics.
It is therefore an object of the present invention to have a foldback circuit which folds back the current to a zero level condition on the occurrence of a sensed short fault in the output of the supply. It is a further object of the present invention to achieve this foldback condition in response to any unusually high current condition whether due to source power surges or current demand of circuitry supplied by the power supply.
A further object of the present invention is to achieve a dynamic monitoring of the condition of the load so as to return the supply to full operating condition at such time as a short fault is eliminated. Yet another object of the present ivention is to provide a power supply having a foldback circuit of high reliability and low noise which is not susceptible to failure in such a way as to harm equipment powered by the supply.